For many years motor control apparatus for controlling valves have contained motors which are energized in one direction by a source of power, returned to the initial position by a spring return and held in some predetermined position by a braking means. Such motor control apparatus is shown in the United States Nelson T. Branche patent 2,052,918 issued Sept. 1, 1936. While the Branche patent discloses a mechanical brake, the use of electrical brakes by applying a direct current source of power to the motor winding is old and is shown in one form in the United States Jean Marie Girard U.S. Pat. 2,434,919 issued Jan. 27, 1948.
The present invention is concerned with a motor control apparatus making use of small inexpensive synchronous inexpensive alternating current powered motors for driving a load through a large ratio gear train by being powered with an alternating current power source to operate the motor in one direction and a spring return to operate the motor in the other direction. A direct current power source is applied to the motor for braking the motor in some predetermined position intermediate its initial and end positions. When a direct current power source is applied to such motors, a permanent magnetization effect takes place so that even though the direct current power source is removed, the braking or holding action remains and the motor may not return to the initial position under the spring return. If a momentary alternating current power source is applied to the motor to demagnetize or deguass the motor, the motor is assured of beingfreed to rotate and can return to the initial position under the spring return.